The proposed investigation is designed to determine (1) the relationships between Sertoli cells and (2) the regulating influence of Sertoli cells on developing germ cells. Two cell-to-cell relationships in the rat, namely the tubulobulbar complexes and the Sertoli-spermatid junction, which have recently been discovered by the principal investigator, will be characterized in the rat, guinea pig and monkey. Data indicate that tubulobulbar complexes form and dissociate in conjunction with cyclic phenomena of the spermatogenic process. It is proposed that their dissociation is a necessary prerequisite for some cell movements in the testis, and thus a regulating influence on the synchronous development of germ cells. To test this hypothesis tubulobulbar complexes will be characterized in the rat utilizing transmission electron microscopy, freeze fracture cytochemical and electron opaque tracer techniques. Studies will also be undertaken to determine at what age tubulobulbar complexes first appear, and whether or not the presence of these structures is dependent upon hormonal stimulation. The Sertoli-spermatid junction, only briefly characterized at this point, forms and dissociates prior to release of the late spermatid. This suggests a functional association of the Sertoli cell with the late spermatid. Sertoli-spermatid junctions will be characterized in the rat utilizing EM, freeze fracture, cytochemical and electron opaque tracer techniques and their formation and dissociation will be correlated with events associated with spermiation. Both types of cell-to-cell relationships are present in a variety of species. A comparative study will be undertaken in the guinea pig and monkey to characterize them in species in which spermatogenesis more closely resembles that in man. The proposed investigation will provide fundamental data which will enhance our understanding of how Sertoli cells regulate the spermatogenic process.